Background: To evaluate the left atrial (LA) volume, and LA systolic (contractile) and diastolic (expansion) functions in different stages of hypertension with or without atrial fibrillation (AF), as well as the effects of good blood pressure control. Methods: A prospective observational study. Individuals including 22 normotensive controls, 23 patients with mild hypertension, 20 with severe hypertension, and 17 with hypertension and paroxysmal AF were recruited for paired echocardiography studies at baseline and 6 months after control of hypertension. Results: With increasing severity of hypertension, left ventricular (LV) diastolic function deteriorated with decreasing LV septal E′/A′ and increasing E/E′ ratios. LA expansion index was reduced in parallel. LA expansion index was correlated positively with LV E′/A′ (r = 0.43, p = 0.022) and inversely with LV E/E′ (r = 0.49, p = 0.009). Significant improvement of LV diastolic function and LA expansion index preceded the reduction of LA volume after blood pressure control. In patients with paroxysmal AF, LA volume reduction was more evident in patients receiving angiotensin-converting enzyme inhibitors or angiotensin II type 1 receptor blockers. Conclusions: With progressive LV diastolic dysfunction in hypertension, there was a corresponding deterioration in LA diastolic function. Effective blood pressure control for 6 months improved LA diastolic function.